1. Technical Field
The present invention relates to an edge adjustment method for performing adjustment such as edge enhancement suited to the characteristics of the input image, an image processing device for performing edge adjustment on the input image by using such method, and a display apparatus, mounted with the image processing device, for displaying the image performed with the edge adjustment.
2. Description of Related Art
Conventionally, a liquid crystal display device for displaying images with a liquid crystal panel is being widespread used as one of the display devices. The liquid crystal display device has an advantage over the display device with a cathode ray tube in that a large and thin display device can be realized. A high-quality image with large amount of data now can be displayed on the display device with increase in the communication speed of the wired or wireless data communication and larger capacity of the recording medium such as DVD or hard disc. In particular, high-definition broadcast is being given attention in recent years, and a high resolution display device capable of displaying an HD (High Definition) image transmitted from a broadcast station by high-definition broadcast is being desired.
However, the current television broadcasts are not all carried out in high-definition broadcast, and a standard broadcast for transmitting the image of lower quality than the HD image, or a so-called SD (Standard Definition) image, and the high-definition broadcast coexist. If the display device corresponding to the display of the HD image displays the SD image, an image with a blurred edge may be displayed, which becomes more significant the larger the display device. In order to transmit the image generated as an SD image in the high-definition broadcast, the SD image is converted to the HD image (so-called, up covert), and then the converted image (hereinafter referred to as up converted image) may be transmitted. The up converted image has a high possibility of being an image with a blurred edge compared to the HD image depending on the image quality of the original SD image, the performance of up conversion, and the like.
Thus, the display device has a function of performing image adjustment process of enhancing the edge of the image before displaying the received image, and displaying the adjusted image, so that the image with the blurred edge is prevented from being displayed. Furthermore, not limited to the television broadcast, and even when displaying the image recorded on a recording medium such as the DVD, the edges are similarly adjusted so that the image with the blurred edge is prevented from being displayed.
Japanese Patent Application Laid-Open No. 2005-176060 proposes a signal processing device capable of performing a high-precision edge adjustment adapted to the frequency band at an appropriate timing when an image of different standard such as SD signal and HD signal is input. In such signal processing device, a data string of a luminance difference of a pixel pair adjacent to each other or with a few pixels in between is first generated for every predetermined number of frames of a luminance signal, a maximum luminance difference is detected from the data string and held, and the data string of the luminance difference is converted to the amount of edge adjustment based on the maximum luminance difference. Then, an edge adjusted signal is generated according to the amount of edge adjustment, and the input image signal and the edge adjusted signal are added by synchronization to thereby adjust the edge of the input image.